Polybrominated diphenyl ethers (PBDEs) and perfluoroalkyl chemicals (PFCs, including perfluorooctane sulfonic acid [PFOS] and perfluorooctanoic acid [PFOA]) are persistent organic chemicals that were introduced several decades ago. Animal studies and limited human studies of PBDEs and PFCs have found evidence for developmental neurotoxicity in children, including thyroid hormone disruption, hyperactivity, delay in neuromotor maturation, and impaired cognition. Although these chemicals are being phased out, humans will still be exposed to PBDEs and PFCs in the environment for decades because these compounds were widely used as flame retardants and surfactants in consumer products. To address the potential adverse health risks of PBDEs and PFCs on fetal, infant, and child neurobehavioral development, the investigators will systematically examine their associations with thyroid function, cognition, learning and memory, motor skills, attention and executive function, and behavior from age 1 to 8 years. The long-term goal is to quantify the roles of PBDE and PFC exposures on child neurobehavior and to inform future prevention efforts. The three specific aims are to: 1) investigate the associations between prenatal and postnatal exposures to PBDEs and thyroid hormones and child neurobehavior; 2) examine the associations between prenatal and postnatal exposures to PFCs and thyroid hormones and child neurobehavior; and 3) assess the environmental exposure to PBDEs through transplacental and lactational routes and indoor dust in children. The investigators will test these associations in the Health Outcomes and Measures of the Environment (HOME) Study, an ongoing NIEHS-funded longitudinal birth cohort of 398 women and their children with current follow-up to 5 years. The investigators will extend the cohort to include an age 8 follow-up clinical visit with comprehensive neurobehavior assessments. The investigators will examine the PBDE and PFC exposures at different developmental stages (in utero at 16 weeks of gestation, ages 3, 5, and 8 years) and child neurobehavior measured at 1, 2, 3, 4, 5, and 8 years using stored serum samples. This longitudinal study will allow the investigators to determine the dose response, windows of susceptibility, and persistence of the association. We will also examine the contribution of PBDE exposures from house dust in a subset of children who have complete sample collection of maternal serum and child serum at 1, 2, and 3 years, along with extensive measures of mouthing behaviors. This research is closely related to the NIH mission to investigate prevalent environmental toxicants and children's neurodevelopment.